Abstract:

A lead frame and an electronic package having improved adhesion between
the lead frame and an encapsulating plastic material is disclosed. The
lead frame can be pre plated having an outer layer comprising a precious
metal such as palladium or gold to which is adhered a self-assembled
monolayer (SAM), such as a SAM derived from an organophosphorus acid. The
organophosphorus acid preferably is a mixture in which the organo groups
are fluoro substituted hydrocarbons and hydrocarbons containing
ethylenically unsaturated groups.

Claims:

1. A lead frame for an electronic package comprising a self-assembled
monolayer adhered directly or indirectly to at least a portion of the
lead frame surface.

2. A lead frame for an electronic package comprising a conductor
surrounding a central aperture; the lead frame having a plurality of
leads extending into the central aperture and a die pad located within
the central aperture having a top and bottom major surface; the top major
surface adapted to receive a die; the lead frame being further
characterized as having a self-assembled monolayer adhered directly or
indirectly to at least a portion of the lead frame surface.

3. The lead frame of claim 2 in which the leads have the self-assembled
monolayer adhered thereto.

4. The lead frame of claim 1 in which the self-assembled monolayer is
adhered to the entire lead frame.

5. The lead frame of claim 2 wherein the self-assembled monolayer is
adhered directly to the die pad.

6. The lead frame of claim 2 wherein the conductor comprises copper or a
copper alloy.

7. The lead frame of claim 2 in which the conductor is selected from
copper, iron, iron alloys and copper plated with a precious metal.

8. The lead frame of claim 7 wherein the precious metal is silver.

9. The lead frame of claim 7 wherein the conductor is plated with an
intermediate layer and to which is adhered a layer of a precious metal.

10. The lead frame of claim 9 in which the intermediate layer is nickel.

11. The lead frame of claim 9 wherein the conductor comprises a copper or
copper alloy base to which is adhered a nickel layer to which is adhered
an intermediate palladium layer and to which is adhered a gold layer.

12. The lead frame of claim 11 in which the nickel layer has a thickness
of 0.1 to 5 microns; the palladium layer has a thickness of 0.01 to 5
microns; and the gold layer has a thickness of up to 200 Angstroms.

13. The lead frame of claim 1 in which the self-assembled monolayer is
derived from compounds selected from organophosphorus compounds,
organosilicon compounds, organosulfur compounds, organocarboxylates and
organoborates.

14. The lead frame of claim 13 in which the self-assembled monolayer is
derived from compounds comprised of several molecular species.

15. The lead frame of claim 2 in which the self-assembled monolayer forms
covalent bonds with the reactive groups on the die pad.

16. The lead frame of claim 15 in which the reactive groups are selected
from oxide and hydroxyl.

17. The lead frame of claim 13 in which the self-assembled monolayer is
derived from an organophosphorus compound.

18. The lead frame of claim 17 in which the self-assembled monolayer is
derived from trivalent phosphorus.

19. The lead frame of claim 17 in which the organophosphorus compound is
selected from a phosphoric acid, a phosphonic acid and a phosphinic acid.

20. The lead frame of claim 13 in which the organophosphorus compounds
have groups of the structure: ##STR00007## where R'' is a hydrocarbon or
substituted hydrocarbon radical having up to 200 carbon atoms and R and
R' are selected from H, a metal, an amine or an aliphatic or substituted
aliphatic radical having 1 to 50 carbon atoms or an aryl or substituted
aryl radical having 6 to 50 carbon atoms; preferably R and R' are H.

21. The lead frame of claim 13 in which the organophosphorus compounds
have groups of the structure: ##STR00008## where R and R' are
independently organic radicals that are aliphatic, aromatic or mixed
aliphatic/aromatic; R and R' are an unsubstituted or a substituted
hydrocarbon having from 1 to 30, such as 6 to 18 carbon atoms.

22. The lead frame of claim 21 where R and R' contain a substituent
selected from fluoro and an ethylenically unsaturated group.

23. The lead frame of claim 22 where the fluoro group is associated with a
perfluoro group and the ethylenically unsaturated group is associated
with a (meth)acrylate group.

24. The lead frame of claim 23 in which the perfluoro group is a
perfluoroalkyl group and the (meth)acrylate group is a (meth)acryloyloxy
group.

25. The lead frame of claim 24 in which the organophosphorus compound is a
mixture of 1 H, 1 H', 2H, 2H' perfluorododecylphosphonic acid and
(meth)acryloyloxyundecylphosphonic acid.

26. The lead frame of claim 21 in which the organophosphorus compounds are
a mixture of organophosphorus compounds comprising at least 10 percent by
weight fluoride substituent and ethylenically unsaturated substituent.

27. The lead frame of claim 26 in which the weight ratio of fluoride
substituents to ethylenically unsaturated substituents is from 1:99 to
80:20.

28. The lead frame of claim 1 in which the self-assembled monolayer is
indirectly adhered to the lead frame through an intermediate
organometallic layer.

29. The lead frame of claim 28 in which the organometallic layer is
derived from a metal alkoxide.

30. The lead frame of claim 28 in which the organometallic layer is
derived from a polymeric metal oxide having unreacted alkoxide and
hydroxyl groups.

31. The lead frame of claim 30 in which the polymeric metal oxide contains
chloride ligands.

32. An electrical package comprising a die bonded with a conductive
adhesive to the die pad of the lead frame of claim 2.

33. The electrical package of claim 32 in which the conductive adhesive is
a metal-filled epoxy adhesive.

34. The electrical package of claim 32 comprising multiple dies.

35. The electrical package of claim 34 in which the multiple dies are in
stacked die configurations.

36. The electrical package of claim 32, which is encapsulated in a plastic
material.

37. The electrical package of claim 32, which is partially encapsulated in
which the leads and the bottom major surface of the die pad are exposed.

38. The electrical package of claim 31 in which the lead frame has a
self-assembled monolayer adhered directly or indirectly to at least a
portion of the lead frame surface and in which the self-assembled
monolayer is derived from organophosphorus compounds of the structure:
##STR00009## where R and R' are independently organic radicals that are
aliphatic, aromatic or mixed aliphatic/aromatic; R and R' are an
unsubstituted or a substituted hydrocarbon having from 1 to 30, such as 6
to 18 carbon atoms.

39. The electrical package of claim 38 where R and R' contain a
substituent selected from fluoro and an ethylenically unsaturated group.

40. The electrical package of claim 39 where the fluoro group is
associated with a perfluoro group and the ethylenically unsaturated group
is associated with a (meth)acrylate group.

41. The electrical package of claim 40 in which the perfluoro group is a
perfluoroalkyl group and the (meth)acrylate group is a (meth)acryloyloxy
group.

42. The electrical package of claim 41 in which the organophosphorus
compound is a mixture of 1 H, 1 H', 2H, 2H' perfluorododecylphosphonic
acid and (meth)acryloyloxyundecylphosphonic acid.

43. The electrical package of claim 38 in which the organophosphorus
compounds are a mixture of organophosphorus compounds comprising at least
10 percent by weight fluoride substituent and ethylenically unsaturated
substituent.

44. The electrical package of claim 43 in which the weight ratio of
fluoride substituents to ethylenically unsaturated substituents is from
1:99 to 80:20.

45. A substrate comprising a layer of gold or palladium having adhered
thereto either directly or indirectly a self-assembled organophosphorus
monolayer.

46. The substrate of claim 45 that is in the form of a multilayer article
in which the gold forms a surface layer to which the self-assembled
monolayer is adhered.

47. The substrate of claim 45 in which the gold layer is thicker than the
self-assembled monolayer.

48. The substrate of claim 47 in which the gold layer has a thickness
greater than 10 Angstroms.

49. The substrate of claim 45 in the form of a multilayer article
comprising a conductive base to which is adhered an intermediate layer to
which is adhered the palladium layer.

50. The substrate of claim 45 in the form of a multilayer article
comprising a conductive base to which is adhered one or more intermediate
layers and to which is adhered the gold surface layer.

51. The substrate of claim 45 in the form of a multilayer article
comprising a copper or copper alloy base to which is adhered an
intermediate nickel layer to which is adhered an intermediate palladium
layer to which is adhered the gold layer.

52. The substrate of claim 51 in which the nickel layer has a thickness of
0.1 to 5 microns, the palladium layer has a thickness of 0.01 to 5
microns, and the gold layer has a thickness of 2-200 Angstroms.

53. The substrate of claim 45 in which the gold or palladium has oxide
groups on its surface.

54. The substrate of claim 45 in which the self-assembled organophosphorus
monolayer is derived from a trivalent phosphorus compound.

55. The substrate of claim 53 in which the self-assembled organophosphorus
monolayer is directly adhered to the gold or palladium layer and forms
covalent bonds with the oxide groups.

56. The substrate of claim 55 in the form of a pre plated lead frame.

57. The substrate of claim 55 in which the self-assembled organophosphorus
monolayer is derived from a pentavalent phosphorus compound.

58. The substrate of claim 57 in which the pentavalent phosphorus compound
is an organophosphorus acid selected from a phosphoric acid, a phosphonic
acid and a phosphinic acid.

59. The substrate of claim 58 in which the organophosphorus acid has
groups of the structure: ##STR00010## where R and R' are independently
organic radicals that are aliphatic, aromatic or mixed
aliphatic/aromatic; R and R' are an unsubstituted or a substituted
hydrocarbon having from 1 to 30, such as 6 to 18 carbon atoms.

60. The substrate of claim 55 in which the self-assembled monolayer is
indirectly adhered to the gold or palladium layer through an intermediate
organometallic layer.

61. The substrate of claim 60 in which the organometallic layer is derived
from a metal alkoxide.

62. The substrate of claim 61 in which the organometallic layer is derived
from a polymeric metal oxide having unreacted alkoxide and hydroxyl
groups.

63. A method of applying a self-assembled monolayer derived from an
organophosphorus acid to a gold or palladium substrate comprising:(a)
applying an organophosphorus acid to the substrate whereby the
organophosphorus acid spontaneously self-assembles in a monolayer
configuration with the acid groups adsorbed on the substrate surface and
the organo groups directed outwardly from the substrate surface.

64. The method of claim 63 in which the surface of the substrate is
subjected to oxidizing conditions before applying the organophosphorus
acid.

65. The method of claim 64 in which the surface of the substrate is
oxidized by treatment with ozone or plasma before application of the
organophosphorus acid.

66. The method of claim 63 in which the substrate is cleaned by treating
with a degreasing composition prior to application of the
organophosphorus acid.

67. The method of claim 63 in which after application of the
self-assembled monolayer, the substrate is given a rinse with an organic
solvent.

68. The method of claim 63 in which during or after application of the
organophosphorus acid, the substrate is exposed to an elevated
temperature.

[0002]The present invention relates to lead frames used in the assembly of
semiconductor devices, and more particularly, to lead frames with
improved adhesion to materials used in semiconductor die packaging,
especially to composite materials used to encapsulate the lead frame.
Another facet of the invention is the formation of a self-assembled
monolayer (SAM) derived from an organophosphorus acid on a gold or
palladium substrate.

BACKGROUND OF THE INVENTION

[0003]A lead frame is used as the electrical connection between a
semiconductor chip and the printed circuit board (and thus to other
electrical components). Lead frames are typically constructed of a base
metal (e.g. copper) onto which subsequent metal layers may be deposited
to enhance properties such as solderability. It is increasingly popular
to plate layers of nickel, palladium and gold in order to get good
adhesion of lead free solder to the lead frame surface. Lead frames are
usually manufactured from a continuous strip of copper or copper metal
alloy (optionally plated with additional layers) onto which a pattern is
repeatedly stamped or etched comprising a central die pad that multiple
inner leads extend out from to outer leads, which form the connection of
the package to the board. Then, an adhesive is dispensed onto the die pad
and a semiconductor chip called a die is placed on top and the adhesive
is cured. Electrical connections are then made between the top of the
semiconductor die and the leads via ultrasonically welded thin gold
wires. This assembly is quite fragile, so it is protected by
encapsulating it in an epoxy molding compound that provides mechanical
durability to the assembly. After curing, the assembly is sectioned from
the adjacent packages and it is connected to a printed circuit board
(PCB) via soldering the leadfingers extending from the assembly to pads
on the PCB. A typical semiconductor device is shown in FIG. 1.

[0004]An example of another semiconductor device is a "QFN" (Quad Flat
Pack No Lead). Such a configuration is shown in FIG. 2 in which the leads
are located on the bottom of the semiconductor device and are exposed as
shown in FIG. 2 for soldering to the circuit board.

[0005]The lead frame is made from a conductive metal typically copper, a
copper alloy, iron, or an iron alloy. Copper is preferred because of its
corrosion resistance, electrical conductivity and solderability. The lead
frame can also be pre plated, so named because the lead frames are plated
prior to semiconductor device assembly. For example, a pre plated lead
frame typically comprises a copper base that is electroplated (partially
or fully) with a layer of nickel and then a thin layer of palladium
followed by a flash layer of gold. FIG. 7 shows a schematic cross-section
of a pre plated lead frame. The pre plated lead frames are desirable
because they allow the use of environmentally friendly lead-free solders
to attach the leads to the circuit board. Also, copper leads such as
shown in FIG. 1 must be presoldered with lead-tin solders before
attachment to the circuit board. This often results in "tin whiskers"
contacting adjacent leads resulting in short circuiting of the
semiconductor device. Pre plated leads such as those described above do
not require presoldering and avoid the tin whisker problem.

[0006]After plating, an electrically and thermally conductive adhesive
(called a `die attach adhesive`) is dispensed onto the central die pad
then a die is placed on top of the adhesive layer. This assembly is then
cured to fix the die to the die pad, providing a conductive path between
the two. During this process, a common problem that occurs is called
`epoxy bleed out` where some of the organic vehicle (epoxy and reactive
diluents, for example) bleed out of the adhesive and spread across the
lead frame surfaces. This bled out layer of organics can have drastically
negative effects on other processes and materials, such as wire
bondability, solderability and mold compound adhesion. Reduction in these
properties typically results in a poorer package that is more susceptible
to environmental stresses and is overall less reliable. Due to this
problem of epoxy bleed there is a pressing need in the industry to
develop materials or methods to limit or stop this phenomenon. After the
die attach step, the semiconductor die is then connected to the
leadfingers by ultrasonically welding gold wires from pads on the die top
to the leadfingers. This is then followed by encapsulation of the entire
assembly in an epoxy molding compound.

[0007]Subsequent to encapsulation, the outer leads of the lead frame are
soldered to a circuit board. During soldering, the temperatures of the
encapsulated package may rise from about 200° C. to about
260° C. Particularly susceptible to this temperature increase are
the QFN semiconductor devices. The rapid increase in temperature and
subsequent cooling stresses the adhesive bond between the lead frame and
the encapsulating plastic often resulting in failure along the
plastic/metal interface. This may lead to moisture entering the assembly
and subsequent failure of the semiconductive device.

[0008]To minimize separation between the encapsulating plastic and the
metallic lead frame, several means to improve the adhesion have been
proposed. These solutions include both means to increase mechanical
adhesion and chemical adhesion. To improve mechanical adhesion, various
configurations of holes, grooves and hemispheres have been formed in both
the leads and the die pad. The holes and deformations increase the
surface area of the lead frame component and also provide crevices for
enhanced mechanical locking. For example, U.S. Pat. No. 4,862,246 to
Masuda et al. discloses forming a series of hemispherical depressions on
the die pad. These depressions increase the adhesion of the die pad to
the molding resin increasing resistance to humidity.

[0009]A layer of nickel applied to a copper alloy lead frame has been
found to increase the strength of the metal/plastic bond as disclosed in
U.S. Pat. No. 4,888,449 to Crane et al. U.S. Pat. No. 4,707,724 to Suzuki
et al. discloses coating the die pad with an alloy of tin/nickel or
iron/nickel to increase adhesive strength.

[0010]Certain chemical solutions also increase the adhesive strength of
the bond between copper and a plastic. U.S. Pat. No. 4,428,987 to Bell et
al. discloses pretreating the copper surface to improve adhesion. The
surface is electrolytically reduced and then coated with a solution such
as benzotriazole. U.S. Pat. No. 5,122,858 discloses coating the lead
frame with a polymer coating such as a polyolefin or a polyimide. U.S.
Pat. No. 7,329,617 also discloses coating the lead frame with a coating
based on a nitrogen-containing polymer such as a melamine-functional
phenolic resin.

[0011]While the prior art processes are somewhat effective to increase the
adhesion between the molding resin and the metal lead frame, the bond is
still often inadequate and failures frequently occur.

SUMMARY OF THE INVENTION

[0012]The present invention provides for a lead frame for an electronic
package comprising a self-assembled monolayer adhered directly or
indirectly to at least a portion of the lead frame surface. Typically,
the lead frame comprises a conductor surrounding a central aperture. The
lead frame has a plurality of leads extending into the central aperture
and a die pad located within the aperture having a top and bottom major
surface. The top major surface of the die pad is adapted to receive a
semi-conductor chip (die). In accordance with the invention, the lead
frame is further characterized as having a SAM adhered directly or
indirectly to at least a portion of the lead frame surface(s) such as to
the bottom major surface or to both the top and bottom major surfaces of
the die pad. The SAM is preferably derived from an organophosphorus acid.
In a particularly preferred embodiment, the organo group comprises at
least in parts fluoro and ethylenically unsaturated substituents.

[0013]In a particular embodiment, the lead frame comprises a copper or
copper alloy base with an intermediate layer of nickel to which is
adhered a subsequent layer of a precious metal such as palladium or gold.

[0014]In another embodiment of the invention, a substrate such as a lead
frame comprises a layer of gold or platinum having adhered thereto either
directly or indirectly a SAM of an organophosphorus acid.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a perspective view of a semiconductor device.

[0016]FIG. 2 is a cutaway perspective drawing of a Quad Flat Pack No Lead
("QFN") semiconductor device.

[0017]FIG. 3 is a plan view of a conductive strip containing a plurality
of lead frames.

[0018]FIG. 4 is a plan view of a semi-conductor chip mounted on one of the
lead frames with the electrodes of the chip connected to the inner lead
portions of the lead frame by conducting wires.

[0019]FIG. 5 is a sectional view along lines 5-5 of FIG. 4 after the
portions within the dotted lines are encapsulated with a plastic
material.

[0020]FIG. 6 is a cross-sectional view of a QFN semiconductor device.

[0021]FIG. 7 is a schematic cross-sectional view of a pre plated lead
frame.

DETAILED DESCRIPTION

[0022]Referring to FIGS. 3 and 4, reference numeral 10 denotes a
conductive metal such as an iron, iron alloy, copper or copper alloy core
strip having a thickness of, for example, 0.25 mm, both sides of which
are optionally pre plated with an intermediate layer such as a layer of
nickel to which is adhered a layer of a precious metal such as silver,
gold or palladium. In a particular embodiment, a copper core can be pre
plated with an intermediate nickel layer to which is adhered an
intermediate palladium layer and to which is adhered a surface layer of
gold. See FIG. 7. Typically the nickel layer has a thickness of 0.1 to 5
microns, the palladium layer has a thickness of 0.01 to 5 microns, and
the gold layer has a thickness of up to 200 Angstroms such as 2 to 200
Angstroms. The strip 10 is punched in several places to provide a
plurality of lead frames 11. The lead frames 11 comprise a chip-mounting
portion (die pad) 14 on which there is mounted, for example, a
semiconductor chip 12 bearing an integrated circuit (die); inner lead
portions 15 for connecting the one side ends of metal wires 13 (FIG. 4),
the other side ends of which are connected to the electrodes of the
semiconductor chip 12; outer lead portions 16 formed by the extensions of
the inner lead portions 15; and supporting portions or connecting
portions 17a and 17b for mechanically stabilizing the die pad 14 and
inner lead portions 15.

[0023]With reference to FIG. 5, the die 12 is bonded on the top major
surface of the die pad 14 by an adhesive agent 18 consisting of, for
example, an epoxy resin. As illustrated in FIG. 5, the strip or core 10
is formed of a conductive metal, both sides of which may be optionally
pre plated as described generally above. Connection wires 13 of gold or
an alloy thereof are bonded to the terminals of electrodes 12a of the
semiconductor chip 12 and connect the semiconductor chip to the free ends
of the inner lead portions 15. The semiconductor chip 12, connection
wires 13 die pad 14 and inner lead portions 15 are all sealed, as shown
in FIG. 5, in a plastic material 19 by the known transfer molding process
or resin casting process. The portions of the lead frame 11 which are
sealed in the plastic material 19 are indicated within the dotted lines
in FIG. 4. Upon completion of the sealing, the supporting portions 17a
are removed by punching and also the outer lead portions 16 and other
supporting portion 17b are cut off of the core 10, thereby providing an
electrical package as shown in FIG. 1. The outer lead portions 16 are
bent in a gull-wing configuration as shown in FIG. 1. Thereafter, the
exposed parts of the outer lead portions 16 are plated with solder to
facilitate subsequent attachment of the electrical package to a circuit
board.

[0024]As mentioned above, the soldering operation stresses the adhesive
bond between the lead frame and the encapsulating plastic often resulting
in failure along the plastic/metal interfacial surface. This is
particularly a problem along the interfacial surface between the bottom
major surface of the die pad 14 and the encapsulating plastic 19, as this
interface is particularly susceptible to degradation by moisture and
heat. To improve the adhesive bond along the plastic/metal interface, the
invention has found that by inserting a SAM 10b adhered to the top and
bottom major surfaces of the die pad significantly increases the strength
and hydrothermal stability of the adhesive bond at the metal/plastic
interface. Alternatively, the SAM can be selectively applied to the
bottom major surface of the die pad. As shown in FIG. 5, the SAM may also
be adhered to the interface between the metal leads 15 and the plastic
encapsulation 19. However, rather than applying the SAM selectively to
various portions of the lead frame that are in contact with the
encapsulating plastic, the SAM is typically applied to the entire lead
frame. By being in monolayer configuration electrical contact between the
connection wires 13 and the inner leads 15 is not adversely affected.

[0025]Another form of the electrical package is shown in FIGS. 2 and 6. A
circuit board 21 carries the electrical package 23. The circuit board may
be a fiberglass-reinforced plastic such as an epoxy resin or a polyester
resin having metal lines or circuits across the surface to which the
electrical package makes electrical contact. As shown in FIG. 6, the die
pad 14 and the leads 16 are not completely encapsulated by the plastic
encapsulant 19 but are located on the bottom surface of the electrical
package 23 where they are exposed and can be attached to the metal
circuits of the circuit board through the leads 16. Attachment of the die
12 to the die pad 14 is through a conductive adhesive layer 18 such as a
metal-filled resin, typically, a silver-filled epoxy resin, and wire
bonding of the die to the leads 16 through metal wires 13 is as described
above. The plastic encapsulant 19 is also as described above. Adhesive
bond failure occurs principally in the circled area shown in FIG. 6.
Insertion of the SAM 10b along the surfaces of the die pad improves the
adhesive bond without interfering with the electrical conductivity as
generally described above. The electrical packages shown in the drawings
and described above show single dies. However, the electrical packages
can have multiple dies such as multiple dies in stacked configurations.

[0026]A problem associated with metal-filled adhesives is adhesive resin
bleed out. Adhesive resin components, such as low molecular weight epoxy
components and/or crosslinking agents, separate from the bulk adhesive
when it is applied between the die 12 and the die pad 14 during a bonding
step. The separated resinous materials flow out from the edges of the
adhesive and wets adjacent surfaces. If the resin bleed flows on to
connection wires or solder pads, it may interfere with or even prevent
the formation of wire bonds or solder joints, also possibly causing epoxy
molding compound delamination, uneven package stress distribution, low
moisture resistance, and ultimately poor package reliability, often
resulting in circuit failure.

[0027]Adhesive resin bleed out can be minimized and eliminated by
selection of an appropriate SAM as described below.

[0028]The lead frame typically has functional groups on its surface that
are reactive with functional groups such as reactive functional groups
associated with the SAM, for example, acid groups associated with SAMs
such as organophosphorus SAMs such as derived from trivalent and
pentavalent phosphorus compounds, particularly pentavalent phosphorus
compounds such as organophosphorus acids such as p-phenol phosphonic
acid. Typical functional groups on the lead frame that would react with
phosphonic acids are metal oxygen species such as M=O, M-OH, M-O-M.
Alternatively, the SAM could be comprised of trivalent phosphorous
species such as (4-hydroxyphenyl)-diphenylphosphine that can form
covalent bonds with zero valent metal species.

[0029]Many of the substrates such as copper and iron have oxide and/or
hydroxyl groups on their surface. Other substrates such as gold or
palladium typically have metal oxygen species on the surface, the
concentration of which can be increased by exposure to a plasma or by
exposure to ozone.

[0030]The SAM can be derived from an organophosphorus compound,
organosilicon compound, organosulfur compound, organocarboxylates and
organoborates. Organophosphorus compounds are preferred. The SAM can be
derived from compounds comprising a single molecular species or several
molecular species. The compound may be monomeric, oligomeric or
polymeric.

[0031]Examples of suitable organophosphorus compounds are organophosphoric
acids, organophosphonic acids and/or organophosphinic acids including
derivatives thereof. Examples of derivatives are materials that perform
similarly as acids such as acid salts, acid esters and acid complexes.
The organo group of the organophosphorus acid may be monomeric or
polymeric (that includes oligomeric).

[0032]Typical organophosphorus compounds are those of the structure:

##STR00001##

where R'' is an organic radical such as a hydrocarbon or substituted
hydrocarbon radical that may be monomeric having up to 200 carbon atoms
or polymeric. R and R' are selected from H, a metal, an amine or an
aliphatic or substituted aliphatic radical having 1 to 50 carbon atoms or
an aromatic substituted aromatic radical having 6 to 50 carbon atoms or
mixed aliphatic/aromatic radicals. Preferably R and R' are H.

[0033]Examples of phosphoric acids are compounds or a mixture of compounds
having the following structure:

(R''O)xP(O)(OR')y

wherein x is 1-2, y is 1-2 and x+y=3, R'' is an organic radical such as a
hydrocarbon or substituted hydrocarbon radical that may be monomeric
having up to 200 carbons or polymeric. Examples of monomeric radicals are
those having a total of 1-50, such as 6-50 carbons. R' is H, a metal such
as an alkali metal, for example, sodium or potassium or lower alkyl
having 1 to 4 carbons, such as methyl or ethyl. Preferably, a portion of
R' is H. R'' can be aliphatic, substituted aliphatic, aromatic or mixed
aliphatic/aromatic radicals. R'' can be unsubstituted or substituted. R''
can have terminal or omega groups such as fluoro such as perfluoro and
functional groups such as ethylenically unsaturated groups, hydroxyl,
carboxylic acid or amine groups that are reactive with the functional
groups such as epoxy groups of the encapsulating plastic and epoxy groups
of metal-filled epoxy resin adhesives.

[0034]Example of monomeric phosphonic acids are compounds or mixture of
compounds having the formula:

##STR00002##

wherein x is 0-1, y is 1, z is 1-2 and x+y+z is 3. R" is organic radical
such as a hydrocarbon or substituted hydrocarbon radical that may be
monomeric having up to 200 carbon atoms or polymeric. Examples of
monomeric radicals are those having a total of 1-50, such as 6-50
carbons. R' and R are H, a metal, such as an alkali metal, for example,
sodium or potassium or lower alkyl having 1-4 carbons such as methyl or
ethyl or a base such as an amine. Preferably at least a portion of R' and
R is H. R can be aliphatic, aromatic or mixed aliphatic/aromatic. R'' can
be aliphatic, substituted aliphatic, aromatic, substituted aromatic or
mixed aliphatic/aromatic radicals unsubstituted or substituted. R'' can
have terminal or omega groups such as fluoro such as perfluoro and
functional groups such as ethylenically unsaturated groups, hydroxyl,
carboxylic acid or amine groups that are reactive with the functional
groups such as epoxy groups of the encapsulating plastic and epoxy groups
of metal-filled epoxy resin adhesives.

[0035]Example of monomeric phosphinic acids are compounds or mixture of
compounds having the formula:

##STR00003##

wherein x is 0-2, y is 0-2, z is 1 and x+y+z is 3. Preferably, R''' and
R'' are each independently organic radicals such as a hydrocarbon or
substituted hydrocarbon radical that may be monomeric having up to 200
carbon atoms or polymeric. Examples of monomeric radicals are those
having a total of 1-50, such as 6-50 carbons. R' is H, a metal, such as
an alkali metal, for example, sodium or potassium or lower alkyl having
1-4 carbons, such as methyl or ethyl. Preferably a portion of R' is H.
The organic component of the phosphinic acid (R, R'') can be aliphatic,
substituted aliphatic, aromatic, substituted aromatic or mixed
aliphatic/aromatic. R''' and R'' can be unsubstituted or substituted.
R''' and R'' can have terminal or omega groups such as fluoro such as
perfluoro and functional groups such as ethylenically unsaturated groups,
hydroxyl, carboxylic acid or amine groups that are reactive with the
functional groups such as epoxy groups of the encapsulating plastic and
epoxy groups of metal-filled epoxy resin adhesives.

[0037]In addition to the monomeric organophosphorous acids, oligomeric or
polymeric organophosphorous acids resulting from self-condensation of the
respective monomeric acids may be used.

[0038]Preferably, at least a portion of the organo groups (R'' and R''')
in the structures above contain fluoride substituent and ethylenically
unsaturated substituent such as acryloyloxy and methacryloyloxy,
hereinafter designated as (meth)acryloyloxy. When both fluoride and
ethylenically unsaturated substituents are present in organophosphorus
acid component, adhesive resin bleed out is significantly minimized and
may even be avoided. Preferably, at least 10 percent such as 20 to 80
percent of the organophosphorus component comprises fluoride substituent
and ethylenically unsaturated substituent. The percentage being on a
weight basis based on weight of fluoride and ethylenically unsaturated
group (CH2═CH═) divided by total weight of the
organophosphorus acid component. The weight ratio of fluoride groups to
ethylenically unsaturated groups in the organophosphorus component is
typically from 1:99 to 80:20.

[0039]Preferably, the organo fluoro group is a perfluoro group such as a
perfluoroalkyl group such as 1H, 1H', 2H' perfluorododecylphosphonic
acid.

[0040]Preferably, the ethylenically unsaturated group is a (meth)acryloyl
group such as a (meth)acrylate functional alkyl group such as
11-(meth)acryloyloxyundecyl. A specific organophosphorus compound is
11-acryloyloxyundecylphosphonic acid.

[0041]For application to the lead frame, the organophosphorus compound is
dissolved in a liquid diluent, however it can also be applied via vacuum
evaporation. The concentration is typically dilute, for example, no
greater than 10 percent on a weight/volume basis, and preferably is
within the range of 0.01 to 1.0 percent. The percentages are based on
total weight or volume of the solution.

[0042]Examples of suitable diluents are water or hydrocarbons such as
hexane isooctane and toluene; ketones such as methyl ethyl ketone;
alcohols such as methanol, ethanol and isopropanol; and ethers such as
tetrahydrofuran.

[0043]The solution of the organophosphorus compound can be applied to the
surface of the lead frame by dipping, rolling, spraying, printing,
stamping, or wiping. After application of the organophosphorus compound,
the diluent is permitted to evaporate, with or without wiping during
evaporation, preferably at ambient temperature, or optionally by the
application of heat.

[0044]The resultant layer is typically thin, having a thickness of about
100 nanometers or less , such as 0.5 to 100 nanometers.

[0045]It is believed that the organophosphorus compound forms a SAM on the
surface of the substrate. The self-assembled layer is formed by the
adsorption and spontaneous organization of the organophosphorus compound
on the surface of the lead frame. The organophosphorus compounds are
amphiphilic molecules that have two functional groups. The first
functional group, i.e., the head functional group, is an acid group that
covalently bonds to the lead frame through reaction of the oxide and/or
hydroxyl groups. The second functional group, i.e., the tail, the organo
groups extend outwardly from the surface of the substrate. It is believed
that in this configuration the monolayer, although very thin, is very
effective in promoting adhesion of the metal/plastic interface. The thin
monolayer configuration also does not affect the electrical conductivity
associated with the wire bonding or attachment of the semiconductor
device to the circuit board.

[0046]As mentioned above, the organophosphorus compound can be applied
directly to the lead frame or can be applied indirectly to the substrate
through an intermediate organometallic coating. When better adhesion and
durability is desired, an organometallic coating may be applied to the
lead frame, followed by application of the organophosphorus compound.

[0047]The organometallic compound is preferably derived from a metal or
metalloid, preferably a transition metal, selected from Group III and
Groups IIIB, IVB, VB and VIB of the Periodic Table. Transition metals are
preferred, such as those selected from Groups IIIB, IVB, VB and VIB of
the Periodic Table. Examples are tantalum, titanium, zirconium,
lanthanum, hafnium and tungsten. The organo portion of the organometallic
compound is selected from those groups that are reactive with functional
groups, such as acid groups (or their derivatives) of the
organophosphorus compound. Also, as will be described later, the organo
group of the organometallic compound is believed to be reactive with
groups on the substrate surfaces being treated such as oxide and hydroxyl
groups. Examples of suitable organo groups of the organometallic compound
are alkoxide groups containing from 1 to 18, preferably 2 to 4 carbon
atoms, such as ethoxide, propoxide, isopropoxide, butoxide, isobutoxide,
tert-butoxide and ethylhexyloxide. Mixed groups such as alkoxide, acetyl
acetonate and chloride groups can be used.

[0048]The organometallic compounds can be in the form of simple
alkoxylates or polymeric forms of the alkoxylate, and various chelates
and complexes. For example, in the case of titanium and zirconium, the
organometallic compound can include:

[0049]a. alkoxylates of titanium and zirconium having the general formula
M(OR)4, wherein M is selected from Ti and Zr and R is C1-18
alkyl,

[0050]b. polymeric alkyl titanates and zirconates obtainable by
condensation of the alkoxylates of (a), i.e., partially hydrolyzed
alkoxylates of the general formula RO[M(OR)2O--]x-1R, wherein M
and R are as above and x is a positive integer,

[0051]c. titanium chelates, derived from ortho titanic acid and
polyfunctional alcohols containing one or more additional hydroxyl, halo,
keto, carboxyl or amino groups capable of donating electrons to titanium.
Examples of these chelates are those having the general formula

Ti(O)a(OH)b(OR')c(XY)d

wherein a=4-b-c-d; b=4-a-c-d; c=4-a-b-d; d=4-a-b-c; R' is H, R as above or
X-Y, wherein X is an electron donating group such as oxygen or nitrogen
and Y is an aliphatic radical having a two or three carbon atom chain
such as

[0056]d. titanium acylates having the general formula
Ti(OCOR)4-n(OR)n wherein R is C1-18 alkyl as above and n
is an integer of from 1 to 3, and polymeric forms thereof,

[0057]e. mixtures thereof.

[0058]The organometallic compound is usually dissolved or dispersed in a
diluent. Examples of suitable diluents are alcohols such as methanol,
ethanol and propanol, aliphatic hydrocarbons, such as hexane, isooctane
and decane, ethers, for example, tetrahydrofuran and dialkyl ethers such
as diethyl ether. Alternatively, the organometallic compound can be
applied by vapor deposition techniques.

[0059]Also, adjuvant materials may be present with the organometallic
compound and the diluent (organometallic compositions). Examples include
stabilizers such as sterically hindered alcohols, surfactants and
anti-static agents. The adjuvants if present are present in amounts of up
to 30 percent by weight based on the non-volatile content of the
composition.

[0060]The concentration of the organometallic compound in the composition
is not particularly critical but is usually at least 0.01 millimolar,
typically from 0.01 to 100 millimolar, and more typically from 0.1 to 50
millimolar.

[0061]The organometallic treating composition can be obtained by mixing
all of the components at the same time or by combining the ingredients in
several steps. Since in some cases, the organometallic compound is
reactive with moisture, care should be taken that moisture is not
introduced with the diluent or adjuvant materials and that mixing is
conducted in a substantially anhydrous atmosphere.

[0062]The organometallic composition can be applied to the substrate
surface by conventional means such as immersion coating such as dipping,
rolling, spraying or wiping to form a film. The diluent is permitted to
evaporate. This can be accomplished by heating to 50-200° C. or by
simple exposure to ambient temperature, that is, from 20-25° C. It
is believed that the resulting film is in the form of a polymeric metal
oxide in multilayer form with unreacted alkoxide and hydroxyl groups.
This is accomplished by depositing the film under conditions resulting in
hydrolysis and self-condensation of the alkoxide. These reactions result
in a polymeric coating being formed that provides cohesive strength to
the film. The conditions necessary for these reactions to occur is to
deposit the film in the presence of water, such as a moisture-containing
atmosphere, however, these reactions can be performed in solution by the
careful addition of water. The resulting film has some unreacted alkoxide
groups and/or hydroxyl groups for subsequent reaction and covalent
bonding with the organophosphorus over layer material. However, for
readily co-reactive groups, ambient temperatures, that is, 20° C.,
may be sufficient. Although not intending to be bound by any theory, it
is believed the polymeric metal oxide is of the structure:

[M(O)x(OH)y(OR)z]n

where M is the metal of the invention, R is an alkyl group containing from
1 to 30 carbon atoms; x+y+z=V, the valence of M; x is at least 1, y is at
least 1, z is at least 1; x=V-y-z; y=V-x-z; z=V-x-y; n is greater than 2,
such as 2 to 1000. Optionally, the organometallic film may also contain
chloride ligands.

[0063]The resulting film typically has a thickness of 0.5 to 100
nanometers. For other applications, thicker films can be used. When the
organometallic compound is used neat and applied by chemical vapor
deposition techniques in the absence of moisture, a thin metal alkoxide
film is believed to form. Polymerization, if any occurs, is minimized and
the film may be in monolayer configuration. When the organometallic
compound is subjected to hydrolysis and self-condensation conditions as
mentioned above, thicker films are formed.

[0064]Although not intending to be bound by any theory, it is believed the
functional groups such as the acid or acid derivative groups of the
organophosphorus compound covalently bond with the hydroxyl or alkoxide
group of the organometallic coating, resulting in a durable film. It is
believed that the organophosphorus compounds form a self-assembled layer
that may be at least in part a monolayer on the surface of the substrate
as generally described above.

[0065]Prior to application of the organophosphorus compound and/or the
organometallic compound, the substrate is cleaned such as by a degreasing
step particularly if the substrates have been in an environment where
they have accumulated hydrocarbon films. A dip with an alcoholic solvent
such as isopropyl alcohol may be used.

[0066]Also after application of the organophosphorus compound and/or the
organometallic compound, the substrate may be given a post rinse to
remove excess material. A post rinse with an organic solvent such as
isopropyl alcohol may be used.

[0067]With pre plated lead frames such as those described above having a
gold or platinum surface layer, the formation of a SAM with
organophosphorus compounds was surprising. Formerly it was believed that
to form monolayers on gold surfaces, thio compounds had to be used. It
was believed that gold and palladium substrates had insufficient oxide
and/or hydroxyl groups on their surface for monolayer self-assembly of an
organophosphorus acid. However, it has been found that the SAMs derived
from organophosphorus acids such as those described above do form on gold
and palladium substrates. Either these substrates contain sufficient
native oxide and/or hydroxyl groups or SAM formation is occurring by a
different mechanism. Optionally gold or palladium substrates can be
subjected to oxidizing conditions by treatment with an oxygen-containing
plasma or by exposure to ozone prior to treatment with the SAM
composition.

[0068]Whereas particular embodiments of this invention have been described
above for purposes of illustration, it will be evident to those skilled
in the art that numerous variations of the details of the present
invention may be made without departing from the invention as defined in
the appended claims.